Colorimetric radiation detector

ABSTRACT

A low cost, rapid, flexible radiation detector uses inorganic metal halide precursors and dyes that respond to self-quenching hybrid scintillation. Remote, high-contrast, laser sensing can be used to determine when exposure of the detector to radiation occurs (even temporally).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/803,880, filed Feb. 11, 2019, which is incorporated herein byreference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Contract No.DE-NA0003525 awarded by the United States Department of Energy/NationalNuclear Security Administration. The Government has certain rights inthe invention.

FIELD OF THE INVENTION

The present invention relates to radiation detection and, in particular,to a direct-reading colorimetric radiation detector.

BACKGROUND OF THE INVENTION

Current dosimeters (radiographic films, scintillation detectors, ionchambers) suffer many drawbacks: difficulty interpreting signals, highcost, complexity of operation, and, they are often single-pointdetectors. Colorimetric radiation detectors produce a change in color orabsorption when exposed to radiation due to the presence of one or morephotochromic dyes in the detector. A leading sensing mechanism is theradiation-induced fluorescence quenching of the organic dye4,4′-di(1H-phenanthro[9,10-d]imidazol-2-yl)-biphenyl (DPI-BP). See J.-M.Han et al., J. Am. Chem. Soc. 136, 5090 (2014). This compound is highlyfluorescent in chlorinated solvents (e.g., CHCl₃, CH₂Cl₂) until exposedto >0.01 Gy gamma-radiation. The radiation stimulus generates freeradicals (.H, .Cl) from decomposition of the chlorinated solvent. Someof the in situ generated radicals form HCl molecules which then reactwith the DPI-BP to generate a salt at the imidazole linkage(HNC₅H₃N.HCl) of the DPI-BP complex. The salts favor π-π stacking whichleads to molecular aggregation and quenching of the fluorescentactivity. While this is an acceptable process, the need for a hazardousCl-based solvent to quench the fluorescence limits its utility indifferent surfaces or architectures. Further, these relativelyinexpensive materials suffer from poor sensitivity and only function inthe liquid state.

SUMMARY OF THE INVENTION

The present invention is directed to a colorimetric (direct reading)radiation detector, comprising a metal halide that decomposes onexposure to radiation and a dye molecule whose fluorescence isself-quenched by reaction with a decomposition product of the metalhalide. The metal halide can comprise a high-atomic-number metal halide,such as bismuth chloride. The dye can be any number of quenchable dyes,such as fluorescein. The direct reading detector does not require exsitu heating and reading with a photomultiplier detector, as is requiredwith thermoluminescence devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will refer to the following drawings, whereinlike elements are referred to by like numbers.

FIG. 1 is an illustration of the radiation-induced fluorescencequenching method of the present invention.

FIG. 2 is an illustration of an exemplary radiation-induced fluorescencequenching system comprising a metal chloride and fluorescein dyemolecule that can be used for the remote detection of radiation.

FIG. 3A is a photograph of a filter paper sample impregnated with anaqueous solution of 6-carboxyfluorescein and BiCl₃ with aradiation-blocking mask defining a thunderbird image. FIG. 3B is aphotograph of the image after a 10-minute exposure to UV radiation. FIG.3C is a photograph of the image after a one-hour exposure to UVradiation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a radiation-induced fluorescencequenching method and colorimetric radiation detector with enhancedsensitivity/quenching behavior to enable remote detection of radiation.The present invention uses radiation-induced fluorescence quenching oforganic chemical fluorophores and chemical-amplification, rather than aphotomultiplier tube, for detection. The quenched luminosity can beremotely detected using commercial laser probes due to the high-contrastchange upon exposure. When used for radiation detection, the technologycan remotely monitor low doses of radiation that can be easily detectedin a passive, continuous (infinite) mode while encompassing a largephysical area.

In general, the colorimetric radiation detector of the present inventioncomprises a metal halide (MX) that decomposes upon exposure toradiation; and a dye whose fluorescence is quenched by a product (M orX) of the metal halide decomposition, as shown in FIG. 1. The metalhalide can comprise a high-atomic-number metal, such as ahigh-atomic-number transition metal or a lanthanide series heavy metal,having adequate stopping power to absorb the incident radiation.Preferably, the metal halide comprises a high-atomic-numberpost-transition metal, such as bismuth, lead, or tin. The metal halidecan comprise a halogen that can easily form a free radical, such asfluorine, chlorine, bromine, or iodine. The metal halide can furthercomprise an electron-donating co-ligand, such as an alkoxide. The dyecan be any number of quenchable dyes, such as fluorescein, coumarin, orrhodamine. The metal halide and dye can be dissolved in a commonsolvent. The solvent preferably comprises a Lewis basic solvent, such aswater or an alcohol, such as methanol, ethanol, or propanol.Alternatively, the solvent can be an aromatic solvent, such as tolueneor xylene. The radiation can typically be high-energy ionizing radiationfrom a ultraviolet (UV), X-ray, gamma-ray, or particle source.

As an example of the invention, the organic chlorinated solvent of theprior system of J.-M. Han et al. can be replaced with an inorganic metalhalide, greatly simplifying the system, enhancing its sensitivity, andallowing for more complex geometries to be used as sensors. A possiblemechanism of radiation-induced fluorescence quenching of an exemplarymetal chloride system is shown in FIG. 2. The exemplary method comprisesthe efficient radiolysis production of radicals .Cl from a metalchloride MCl_(n), and the capture of .Cl by dye molecules and subsequentquenching of fluorescent activity. Commercially available metalchlorides (MCl_(n)) and a fluorescein dye molecule (referred to as FDM)can be used. The metal chloride preferably has weak M-CI bonds thatenable the rapid production of .Cl radicals upon exposure to radiation.Homoleptic MCl_(n) does not necessarily offer the best process forhalide formation, therefore an electron-donating co-ligand (i.e.,(OR)_(z)MCl_(n-z)) that promote radicalization can be used. Usingquantum-based computational modeling as a screening tool, fine tuning ofthis system can provide the most sensitive radical MCl_(n) generatorsand receptive dye molecules possible for a specific radiationsource/level.

The formation of .Cl can be generated under similar conditions, but asolid or liquid sensor can be used. This allows for production of moreaccessible and less obvious sensors (i.e., paint). The use of MCl_(n)precursors as a source of .Cl is well established with several beingstable; however, these typically involve complex ligands bound to themetal. As an example, commercially available MCl_(n) mixed with FDMs canbe as a radiation-induced fluorescence quenching system for remotedetection of gamma-radiation. High-atomic-number MCl_(n) precursors canbe used as a source of .Cl in the presence of FDMs. A high number ofcoordinated Cl can be radicalized, ensuring an economical use of theinorganic precursor. A radiation-induced fluorescence quenching systemfor remote detection of low levels of gamma or other forms of radiationcan thereby be created through computationally refined MCl_(n)/FDMsystems, providing enhanced sensitivity coupled with an extremelyversatile material form enabling significant improvements in the remotedetection of gamma-radiation.

As an example of the invention, the colorimetric radiation detector cancomprise bismuth chloride, which is soluble in water or methanol andeasily forms a chloride radical upon excitation by a radiation source,and a fluorescein dye. A photographic image of a colorimetric radiationdetector showing a change in color of the sensor material after exposureto ultraviolet radiation is shown in FIGS. 3A-3B. A 10 weight % aqueoussolution of 6-carboxyfluorescein (6CF) was added to 0.1 molar solutionof BiCl₃, either aqueous or methanol. The mixture was deposited ontoWhatman filter paper. FIG. 3A is a photograph showing a sample of paperimpregnated with the 6CF/BiCl₃ solution, with a radiation blocking metalmask defining a thunderbird image. FIG. 3B is a photograph of the sampleafter a ten minute exposure to 395 nm UV ionizing radiation. The maskhas been removed to demonstrate color change resulting from thefluorescence quenching of the 6CF dye. FIG. 3C is a photograph of thesample after a one-hour exposure to the UV radiation.

The present invention has been described as a colorimetric radiationdetector. It will be understood that the above description is merelyillustrative of the applications of the principles of the presentinvention, the scope of which is to be determined by the claims viewedin light of the specification. Other variants and modifications of theinvention will be apparent to those of skill in the art.

We claim:
 1. A colorimetric radiation detector, comprising: a metalhalide that decomposes on exposure to radiation; and a dye whosefluorescence is quenched by a product of the metal halide decomposition.2. The colorimetric radiation detector of claim 1, wherein the metalhalide comprises a high-atomic-number post-transition metal halide. 3.The colorimetric radiation detector of claim 2, wherein thepost-transition metal halide comprises bismuth chloride.
 4. Thecolorimetric radiation detector of claim 1, wherein the metal halidecomprises a high-atomic-number transition metal halide or a lanthanideseries heavy metal halide.
 5. The colorimetric radiation detector ofclaim 1, wherein the metal halide comprises a metal chloride.
 6. Thecolorimetric radiation detector of claim 1, wherein the metal halidefurther comprises a co-ligand.
 7. The colorimetric radiation detector ofclaim 6, wherein the co-ligand comprises an alkoxide.
 8. Thecolorimetric radiation detector of claim 1, wherein the dye comprisesfluorescein.
 9. The colorimetric radiation detector of claim 1, furthercomprising a solvent and wherein the metal halide and the dye aredissolved in the solvent.
 10. The colorimetric radiation detector ofclaim 9, wherein the solvent comprises a Lewis base solvent.
 11. Thecolorimetric radiation detector of claim 10, wherein the Lewis basesolvent comprises water or an alcohol.
 12. The colorimetric radiationdetector of claim 9, wherein the solvent comprises an organic solvent.13. The colorimetric radiation detector of claim 12, wherein the organicsolvent comprises toluene or xylene.
 14. A method for detectingradiation, comprising: providing a colorimetric radiation detector, thedetector comprising: a metal halide that decomposes on exposure toradiation; and a dye whose fluorescence is quenched by a product of themetal halide decomposition; exposing the colorimetric radiation detectorto radiation; and detecting a change in color of the colorimetricradiation detector.